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Written By: Jeff
Project video at http://www.flickr.com/photos/81 9041 1(5>N07...
For my son's fourth birthday, we decided on a fire truck theme. We started the party with a
tour of a fire station and then went back to the house for a firefighters' obstacle course and
the creation of several Duplo fire trucks (and of course, cake, ice cream, and fellowship). In
keeping with the theme, my wife made several firefighter-themed treats and props.
Being largely unable to bake, my most significant party theme contribution was repurposing
my old car launcher invention ( http://www.flickr.com/photos/819041 1(5)N07... ) to be used as
a MatchBox-scale fire station.
I originally made the car launcher to live at the bottom of our coat closet and accept car-
dispensing commands from distant relatives via our family blog. For our fire-themed party, I
mounted it in the bottom of our living room entertainment center and built a cardboard fire
station facade. I swapped out the old PHP/Processing/AppleScript/BS2 control scheme for a
an Arduino-based radio-monitoring scheme. I mounted a trunk-tracking radio scanner (from
one of my other hobbies, amateur radio) on the underside of the car launcher. I programmed
the scanner to scan the Alert talk groups for our county fire department, our city fire
department, and our county emergency medical service. The Alert talk groups are just for
relaying dispatch orders with a computer-synthesized voice. No human voices are
transmitted there, just a brief alert warble followed by the orders to get moving. Sticking to
merely the fire department talk groups would have been ideal, but there might not have been
enough fire calls during the party to dispatch all of our toy trucks.
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I programmed the Arduino to monitor the voltage of the scanner's audio and operate the fire
truck launcher when a call comes through. I have the scanner's internal speaker muted and
the Arduino controls a relay that feeds an external speaker only when a call comes through
for which it is dispatching a truck. I have a minimum-time-between-launches set in the code
so the launcher doesn't empty itself too fast. The launcher uses a single continuous-rotation
servo to open a door that is mounted on a drawer slide. An IR emitter and detector are used
to sense each stopping point, and small switches are used to detect full open and full close.
I mounted a couple of red LEDs on the cardboard fire station facade to add to the effect and
to warn nearby partygoers that a fire truck is forthcoming.
The net effect of all this is that when a real fire truck or ambulance is dispatched in Wake
County, our tiny fire station plays the same radio call the firefighters hear, at the same time
they hear it, and shoots out a toy fire truck into our living room for the entertainment of our
Step 1 — Dispatchatron
• Gravity gets the cars moving. The
launching mechanism just moves
the door out of the way.
• I used a fancy trunk-tracking
scanner to monitor several talk
groups. In my area, the emergency
services use atrunking radio
system. They also simulcast the
alert talk groups on a single VHF
frequency, though, so I could have
used a simpler radio if I had one.
• A fixed continuous-rotation servo
controls the sliding drawer by
moving the VEX chain through the
gears, stopping when the IR pair
detects a stop or when the limit
switches detect full open or close.
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• I whipped up the facade out of
cardboard and construction paper. I
mounted LEDs on either side of the
door for a nice flashing effect. The
sign you see to the left is one of
many we had to give various food-
information to partygoers.
• Here is my Dispatchatron mounted
to the back side of the
entertainment center. I'm a tad
embarrassed by my sloppy wiring,
but I had to make sure it was ready
in time for the birthday party. I got
a majorly sore back reaching back
in here for troubleshooting and the
addition of the LEDs.
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• After installing the Dispatchatron
behind the entertainment center
and getting all the various
alignments and clearances perfect,
I realized that the Arduino was not
driving my cardboard facade's
LEDs brightly enough to be seen
during the day. I threw together a
couple PNP transistor boosters to
reach back and plug in. I ran the
red wire off the emitter to plug into
my +5v rail, a 10k resistor off the
base to plug into the Arduino
output, and a snipped-off piece of
female header into which I plugged
the wire going to the LED.
This document was last generated on 2012-11-01 06:02:26 PM.
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